The output from cathode follower V5 is coupled by capacitor C12
to the output amplifier.
3
-4
OUTPUT AMPLIFIER
The output amplifier includes tubes V8 and V9.
The signal incom-
ing from the selective amplifier is passed to the grid of V8 via
variable resistor
R57, the setting of which is adjusted by the AM-
PLITUDE control on the control panel. Thus, by adjusting the in-
put to the output amplifier, the AMPLITUDE control becomes, in
effect, the gain control for the instrument.
Pentode V8 operates as
a
driver for high-mu pentode V9, the power
output tube.
Pentode V9
is connected as
a
triode to allow the tube
to work into very low impedance loads without generating appreci-
able distortion. Negative feedback from
V9, applied via capacitor
C19 and resistor R67 to the cathode of
V8, is used to minimize
distortion.
The output of V9 is passed, via a rectifier-type voltmeter, an
attenuator, and an impedance -matching transformer to the OUT
-
PUT binding posts.
3-5 VOLTMETER
The voltmeter circuit includes variable resistor
R69, a germanium
diode full-wave rectifier, and a one-milliampere meter connected
across the rectifier bridge. Resistor R69 is provided for adjust-
ment of the meter calibration. The meter is arranged to indicate
the output voltage directly in volts across 600 ohms and in dbm,
with
0 dbm equal to
1
milliwatt into 600 ohms.
3-6
ATTENUATOR
The attenuator has three sections, each of which is controlled by
its own dial.
One section is of an L-type configuration, with ten
steps of.
1 db each. The other two sections are bridged-T configu-
rations, one of ten 1 db steps and the other of ten 10 db steps. The
three attenuators provide from
.
1
db
to 111 db attenuation of the
output voltage.
3-7 IMPEDANCE-MATCHING TRANSFORMER
Connections to impedance -matching transformer T2 are established
by the IMPEDANCE switch,
S2. In the 50,
150, and 600 positions
of the switch: (1) the output voltage is passed to the primary winding
of transformer T2 and (2) the secondary of T2 is connected to the
OUTPUT binding posts.
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